The present invention relates to the field of tools that utilize wafers in cassettes; more specifically, it relates to a method and apparatus for calibrating sensors that detect wafer protrusion from a wafer cassette.
Many wafer cassette based tools have an optical wafer protrusion sensor in the load/unload chamber to detect a wafer which is protruding too far out of its slot after the cassette has been loaded into the load/unload chamber. Wafer protrusion is caused by the wafer not being fully seated in its slot in the wafer cassette. After the cassette is loaded, the thru beam sensor will alarm the tool if there are any wafers breaking the beam and prevent the tool from running. If not calibrated correctly, the handling of this wafer into the tool can cause mishandling of the wafer resulting in a breakage or tool errors. Currently, in order to calibrate the sensors, the wafer is manually pushed out of its slot an estimated distance or a measured distance using a flat edge and ruler to vary the distance with reference to another point on the cassette. This method is not precise and time consuming. Accordingly, there exists a need in the art to mitigate the deficiencies and limitations described hereinabove.